Soloing Rancor without Zader or Rex

Wiggs, Jyn, Bistan, Baze (although any other person with speed down works)
or
wedge, Chaze, Jyn, Bistan
or
teebo, jyn, bistan (pick just about any other two guys)

I have used both of the first two lineups for months with no problems. You can't go full auto, but it works.